There has been a lot of talk about electronic money transactions using an IC card or the like, and there are actually some regions into which this system has been introduced. There has also been known an electronic transaction terminal called VST (Value Service Terminal) as a terminal used for electronic money transactions. This VST has functions such as depositing and withdrawing electronic money, checking a balance on a bank account, and checking transaction histories. The VST is connected to a host computer (HOST) provided in a bank or elsewhere through a communication line.
FIG. 15 is an explanatory view showing a sequence of communication between the VST and the HOST. A cipher for security is used for communications between a VST 500 and a HOST H. When the VST 500 transmits a communication-start signal to the HOST H, the HOST H encrypts an encrypting key "KEY2" using an encrypting key (KEY1), and transmits the encrypted key to the VST 500. The VST 500 decrypts the encrypted encrypting key "KEY2" with a decrypting key (KEY1') held by the VST 500 to acquire "KEY2".
Then, the VST 500 encrypts information for electronic transaction information "A" such as a personal identification number inputted by a user with the acquired encrypting key (KEY2), and transmits the encrypted information to the HOST H. The HOST H decrypts the encrypted electronic-transactional information "A" with a decrypting key (KEY2') to acquire the electronic-transactional information "A".
FIG. 16 is an explanatory view showing general configuration of the VST 500 and the HOST H. The decrypting key (KEY1') in the sequence is previously stored on a memory 501 of the VST 500. The memory 501 of the VST 500 temporarily stores thereon an encrypting key (KEY2) sent from the HOST H. The VST 500 has an input section 502 through which electronic-transactional information is inputted. While the HOST H has the encrypting key (KEY1), encrypting key (KEY2), and the decrypting key (KEY2') stored on a memory HM thereof. In addition, a program for the sequence is stored on each of the memories 501 and HM of the VST 500 and HOST H respectively, and CPUs 503 and HC are actuated according to the program. The VST 500 and the HOST H are connected to each other through interface circuits 504 and HI.
There has been known an information processing unit disclosed in Japanese Patent Laid-Open Publication No. HEI 4-128948 as a device for maintaining security of the information stored on a memory. This information processing unit is designed to cut off, when a cover for a main unit thereof is taken off, power to supply to a buttery-backup memory so that data on the memory is broken. Opening and closing of the cover is detected by a microswitch.
In the conventional type of VST 500, however, although the security of electronic-transactional information is ensured by encryption, the electronic-transactional information inputted from the input section 502 for the VST 500 exists as raw data on a circuit until the data is encrypted by the encrypting key (KEY2). For this reason, if the circuit with raw data existing thereon is tampered with to get unauthorized access thereto, electronic-transactional information may be stolen. In addition, if the decrypting key (KEY1') stored on the memory 501 of the VST 500 is illegally read, the contents of the encrypting key (KEY2) sent from the HOST H may leak, which may cause electronic-transactional information to be stolen.
In the information processing unit, the microswitch is set as a trigger, so that data on the memory is broken as soon as the case for the main unit is opened. And for this reason, if the case is not opened but the unit is tampered with by making a hole on the case thereof with a drill or so to get unauthorized access to the circuit, the security is not sufficiently ensured any more. Also, data would be deleted by opening the case for the main unit, so that it is required to set data again even when maintenance is executed to any section nothing to do with the security, which makes the work more troublesome.